Current transformer for high-voltage bushings



CURRENT TRANSFORMER FOR HIGH VOLTAGE BUSHINGS Filed Sept. 1928 5 Sheets-Sheet l TTORNEY.

Sept. 17, 11929. A. Q. AUSTIN CURRENT TRANSFORMER FOR HIGH VOLTAGE BUSHINGS Filed Sept. 1928 5 Sheets-Sheet 2 f 37 3a? 31 I; '30

y\/\/\/\/\ y 38/ f 42 if 36 g 27 if g 23 38) L 5 11$ g Z7 21 03 j m Wffiw 0%1/627/7. INVENTOR ATTORNEY A. O. AUSTIN CURRENT TRANSFORMER FOR HIGH VOLTAGE BUSHINGS Filed Sept. 8, 1928 Sheets-Sheet 3 Sept. 17, 19290 INVENTOR Ausf/n- I a-n/Q ATTORNEY Sept. 17, 1929. A. o; AUSTIN CURRENT TRANSFORMER FOR HIGH VOLTAGE BUSHINGS Filed Sept 8, 1928 5 Sheets-Sheet 4 Fig.4

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A TTORNE Y Sept. 17, 1929. A. o. AUSTIN CURRENT TRANSFORMER FOR HIGH VOLTAGE BUSHINGS I Filed Sept. 8, 1928 5 sheets-she t 5 INVENTOR Arf/vur 0. AuJf/n BYQ; 4L2! l -lyin Patented Sept. 17,, 1929 UNITED STATES PATET OFFICE ARTHUR O. AUSTIN, OF NEAR BARBERTON, OHIO, ASSIGNOR, "BY MESE'E ASSIGN- MENTS, TO THE OHIO BRASS COMPANY, OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY CURRENT TRANSFORMER FOR HIGH-VOLTAGE BUSHING-S Application filed September 8, 1928. Serial No. 304,762.

This invention relates to a construction which may be used in connection with a bushing insulator for diverting a relatively small amount of energy from a high potential conductor which passes through an insulator, for-the purpose of metering, relay operation, synchronizing or other operations where it is not desired to employ an expensive potential transformer and where a comparatively small amount of energy is required.

One object of the invention is to provide an arrangement of the class named which shall be economical to manufacture, efficient in operation, convenient to install and which will not impair the insulation of the device in which it is used.

Another object of the invention is to correct the effect of the magnetic core of the current transformer upon the phase relation of the voltage and current. .Other objects and advantages will appear from the following 'description.

The invention is exemplified in the combination and arrangement of parts shown in the accompanying drawings and described in the following specification, and it. is more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is an elevation with parts in section showing one embodiment of the present invention.

Fig.2 is a view similar to Fig. 1 showing another modification of the invention.

Figs. 3, 4 and 5 are other views similar to Fig. 1 showing other modifications.

Fig. 6 is a somewhat diagrammatic view of another modification.

It is frequently desirable to equip high voltage bushings with current transformers for the operation of relays, metering, and the indication of current flowing in the circuit. Where the magnetic flux set up in a current transformer .of this kind is due to a single turn on the primary side, the flux will be very weak and Where the voltage on the conductor passing throu h the bushing is high, the diameter of the ushing must be large, thus requiring a magnetic core of very large diameler. This tends to reduce the efficiency and accuracy of the current transformer and hence, an improved type of current transformer is very desirable.

. In my previous application, Serial No. 266,275, I have shown one improved type wherein the primary winding, instead of malnng a single turn, is wound around a magnetlocore located in the center portion of the bushing. The secondary of the current transformer may then be made up of a number of turns located inside-of the bushing shell.

This arrangement makes a current trans former which can be used over quite a wide range of current in the primary and still provide an effective volt ampere capacity for the operation of connected equipment such as relays, meters, etc. While the secondary windmg may be connected to a transformer for stepping down or up, the ratio may be readi- 1y changed on the outside of the transformer. My previous application includes means for effecting material changes in the number of turns in the primary so that even though the current in the primary be small, an effective transformer is produced.

Owing to the magnetizing component, the phase angle and ratio of the current transformer will vary much more than in transformers where the magnetic path is shorter.

The present invention deals with an improved method of correcting these deficiencles 1n the current transformer in order that the ratio may be more accurate for metering or other purposes. As the greatest difficulty is encountered at very high voltages where the magnetic path in the current transformer, owing to the size of the bushing, is long, the high voltage can be used to correct characteristics of the current transformer to a considerable extent. I

In theform of the invention illustrated in the accompanying drawings. the invention is shown as applied to the form of current transformer described and claimed in my prior application referred to above. It will be understood, however, that the principles of the present invention may be applied to other forms of current transformers.

Referring to Fig. 1, as explained in my prior application, the numeral 10 designates the lower section and the numeral 11 theupper section of a tubular conductor, the two sections being joined by a dielectric tube 12 to the ends of which the sections 10 and 11 are attached. A laminated soft iron core 13 is disposed within the tube 12 and the ends of the sections 10 and 11 are preferably. swaged or shrunk onto the fiber sleeve 12 and the core 13 so that together the parts 10, 11, 12 and 13 form a rigid mechanical member.

A helical winding 14 isplaced over the iron core 13 and insulating sleeve 12 and the ends of the winding are connected respectively to the conductors 10 and 11 so that the current in passing from one section to the other of the conductor cannot flow in a straight line but must flow around and magnetize the core 13. This increases the magnetic flux in the iron core so that, althoug the current may be weak, the core will be sutficiently magnetized because of the plurality of turns. The tube members 10 and 11 may be used for supporting an insulating baffle 15.

ing 18 which forms the secondary winding of the current transformer. This secondary winding may have any suitable number of turns and may be placed as near the center of the bushing as insulating requirements will permit.

In large oil-filled bushings, the outer dielectric housing members 19 and 20 may readily be placed at a somewhat greater distance from the axis of the bushing than the winding 18. This greater diameter tends to cut down the intensity of the field outside of the bushing and thereby improve thelength efficiency of the bushing and does not interfere with the efficiency of the current transformer, as is the case where the secondary of the current transformer must be slipped over the I outside of the bushing. One end of the winding 18 may be grounded to the flange of the bushing so as to provide charging current or, if desired, a metallized or charging surface 21 may be provided between the winding 18 and the insulating baflle 17. This charging screen will relieve the winding 18 of any electrostatic stress so that it will not be necessary to ground the winding unless desired. The metallized surface or charging screen 21 should not form a short circuit turn encirsome extent, by baflies composed of magnetic material or of material having exceedingly low resistance, such as copper. By keeping the metal parts, such as the flange 22 of the bushing or the housing on which the bushing is mounted, at a considerable distance from the axis of the bushing, a large portion of the magnetic flux will return without cutting the short circuit turn formed by these metal parts. In order to assist in controlling the path of the magnetic flux, the baflle 17 may be wrapped with thin layers of iron as shown at 23, the several layers being insulated from each other so that a short circuit is not formed.

This wrapping is placed outside of the winding 18 and is separated therefrom by an insulating sleeve 24. The Wrapping projects well along the axis of the bushing and will form a return path outside of the winding 18 for a considerable portion of the magnetic flux emanating from the core 13. The magnetic wrapping 23 may be clamped or held by a ring 25 which, in turn, is supported at the J middle of the bushing by a plate 26 secured An outer baffle 17 is surrounded by a windcling the sleeve since a short circuit turn, in

this position, would interfere with the operation of the winding 18.

It is evident that some of the magnetic flux set up by the helix 14 may not return in a path to include all of the turns of the wind-. ing 18 but this will not materially impair the operation of the arrangement so long as the flux cutting-the winding 18 is proportional to the current flowing in the lead 10 for the range of operation of the installation.

The path of the flux may be controlled, to

to the flange 22. The ring 25 and wrapper 23 support the outer baffle 17 The leads and taps for the secondary'winding 18 are brought out through a bushing 27 extending through the side of the housing 20 and are insulated from each other and form an oil tight joint with the housing. The taps may be connected to synchronizing, metering or other apparatus through a transformer 28, or by direct connection.

A jumper 29 is connected to the lower section 10 of the central conductor and extends upwardly through the core 13 and upper section 11 of the tubular conductor and is connected at its upper end to one terminal of a. spark gap 30. The other terminals are insulated from each other and provided with adj ustable discharge points, as shown in the drawing. This provides a gap for limiting the voltage across the windingle which Will break down and relieve the insulation betweenthe two ends of the sections 10 and 11 if abnormal stress is produced by transient disturbances orsurges.

In the form of the invention shown in Fig.

1, the incoming conductor 31 is covered by a rent may be used for magnetizing the core in the bushing by connecting a conductor 34 to the cage which passes down through the bushing and around the core forming a winding 35 and which is then attached to the conductor 10 inside the bushing or may be carried out and attached to the. conductor outside of the bushing. A dielectric sleeve 39 separates the windings 1 1 and 35.

- The direction of winding and current in this corrective winding is such that it will help the main primary current, passing through the bushing, in magnetizing the core of the current transformed. The effectiveness of this current may 'be regulated by changing the electrostatic capacity of the condenser on the outside of the bushing or by changing the number of turns around the core Within the bushing.

Another method of correction, illustrated in Fig. 2, is to place a series transformer 36 in the incoming line. This transformer will be wound with a few turns 37 in the primary side and a considerable number of turns 38 on the secondary side. The secondary ,circuit is completed through the winding 35 which passes around the core in the center of the bushing and a condenser 39 is connected in series in the circuit. Since the current is leading in this condenser, it will have a corrective value on the flux in the main current transformer located in the bushing.

It is evident that the magnetization of the core of the current transformer located in the bushing may be entirely accomplished by using the secondary winding of the transformer. In this case, the transformer located outside the bushing can be provided with taps or a change in ratio so that the effective ratio in the main transformer in the bushing can be changed as desired by simply changing the ratio on the transformer located outside the bushing. in the lead outside the bushing may be supported by the bushing or any place along the lead where it can be conveniently located. Since the diflerences in potential are very small, the several leads entering the bushing will not provide any dificult insulating problem. lt is evident that where the correction method is employed the transformer located in the external lead may be made to develop a considerable voltage on the secondary side so that an efiicient condenser 39 may be used.

This arrangement makes it possible to provide much more energy in the current transformer and operates to offset the effect of the magnetic core on the phase relation of voltage and current.

Discharge gaps 40, 41 and 42 may be provided to protect the various parts spanned by them from excess voltages. A variable resistance 43 may be bridged across the leads to the winding 35 by means of which the current in the winding can be regulated. A resistance 43 in series may also be used for a similar purpose, the two resistances being used either in conjunction with each other or separately.

It is apparent that reactances may be used in conjunction with the resistances 43 and 43' hr in lieu thereof.

In the form of the invention shown in Fig. 3, the conductor 45 is continuous through the bushing and the core 13 is magnetized by a winding 46 energized by a series trans- The current transformer located former 47 in theincoming line. The transformer 47 may be provided wit-h a plurality of primary coils 48 arranged to be connected .-in difierent relations to vary the transformer provided with a primary winding 51 in series with the incoming line and with the secondary winding 52 connected with the winding 53 surrounding the core 13. A condenser 54 is in series with the secondary winding 52 to provide a leading current in the winding 53. This leading current will tend to correct the lag of the magnetic flux in the core 13.

In the form of the invention shown in Fig. 4, the conductor 45 extends continuously through the bushing as in the form shown in Fig. 3. The core 13, in this instance however, is magnetized by means of a coil 55 connected at one end by the main conductor 45 and at the other end to the metallic sleeve 56 disposed outside of the coil 55 and insulated from the coil and conductor 45. Charging current flowing from the conductor 45 to the metallic member 56 will pass through the coil 55 and will magnetize the core 13. This charging current will be leading and will 0dset the efiect of the magnetic core so that the current induced in the winding 18 will be substantially in phase with the induced voltage.

In the form of the invention shown in Fig. 5, the-exciting current is supplied by a winding 14 in series with the main conductor in the manner described in connection with Figs. 1 and 2. The winding 35 is connected at one end to the conductor 10 and the other end is connected to a lead 57 which is brought out through an insulating sleeve 58 and connected through a series of condensers 59 to ground. Charging current will flow from the conductor 10 through the winding 35 and lead 57 to the condenser 59. This will, of i course, be a leading current and will effect a correction of the phase relation of the voltage and current in the secondary winding 18. lit will be apparent that instead of introducing a leading current in the primary side of the current transformer, a correction may be effected in the secondary circuit; or the lead mg current may be introduced in connection with the secondary circuit to supplement the efiect of the correction in the primary circuit.

plied from the charging current for the outermember of the condenser formed by the bushthrough the winding 60, thus producing a corrective effect on the phase relation of the current in the transformer 28.

A limiting gap 61 may-be employed for limiting the'voltage impressed upon the winding 60 and a gap 62 may be used for limiting the voltage between the line 31 and the lead 57.

A reactance 63 and a resistance 64: may be introduced into the correction circuit to regulate the amount of correction so as to obtain the desired phase relation between voltage and current in the circuit of the transformer 28.

Instead of connecting the lead from the winding 35; through condensers to ground, it may be connected through condensers 65, as shown in Fig. 6, to another conductor 66 of a polyphase system.

Other modifications within the spirit andscope of the invention, 'as defined in the appended claims, will readily suggest themselves to those skilled in the art.

I claim: J

1. The combination with a conductor, of a secondary winding forming with said conductor .a current transformer, and supplemental exciting means for said'current transformer for correcting phase displacement.

2. The combination with a conductor, of a secondary winding forming with said conductor a current transformer, a magnetic core for said transformer, and means for supply ing a leading supplemental exciting current to said transformer for correcting the effect of the magnetic circuit of said transformer on the phase relation of the voltage and current of said transformer.

3. The combination with a conductor, of a secondary winding forming with said conductor a current transformer, a magnetic core for said transformer, a condenser arranged to be charged by the current flowing in said conductor, and a supplemental pr mary windingfor said current transformer excited by the charging current of said condenser.

4. The combination with a bushing insulator, of a conductor extending through said insulator, a secondary winding forming with saidconductor a current transformer, a magnetic core member in the field of said transformer, a supplemental primary winding for said transformer, and means for supplying a leading current to said supplemental primary winding.

5. The combination with a bushing insulator, of a conductor extending through said insulator and having a series winding disposed within said insulator, a magnetic core for said winding, a secondary winding forming a transformer with said series winding and magnetic core, and means excited by the current in said conductor for supplying a leading supplemental exciting current to said transformer.

6. The combination with a bushing insulator, of a conductor extending through said insulator,'a magnetic core member arranged within said insulator, a primary winding for magnetizing said core member, a secondary winding forming a transformer with said primary winding and core member, and means for supplying a leading current to said primary winding.

7. The combination with a bushing insulator, of a conductor extending through said insulator, a magnetic core member disposed within said insulator, a primary winding for magnetizing said core member, a secondar winding forming a transformer with said'primary winding and core member, a condenser arranged to be charged by the current of said conductor, and means for directing the charging current of said condenser through said primary winding. v

8. The combination with a bushing insulator, of a conductor extending through said insulator and forming the primary of a current transformer, a secondary winding for said current transformer disposed within said insulator, and means for supplying'a supplemental leading exciting current to said transformer.

9. The combination with a bushing insulator, of a conductor extending through said insulator and forming the primary of a current transformer. a magnetic core member arrangedvin the field of said transformer, a

secondary winding for said transformer, a

supplemental primary winding for said transformer, and a condenser charged by the current in said conductor for supplying leading current to said supplemental primary winding.

10. The combination with a bushing insulator, of a high potentialconductor extending through said insulator and having a primary current transformer winding in series therewith disposed within said insulator, a core member for said winding, a secondary winding disposed within said insulator, a supplemental primary winding disposed within said insulator, and a condenser arranged to be charged by the current flowing in said conductor for supplying leading current to sai supplemental primary winding.

11. The combination with a bushing insulator, of a conductor extending through said insulator, a transmission line connected with said conductor, a condenser associated with said transmission line, a current transformer energized by said conductor, and means for supplying supplemental energizing current from said condenser to said current transformer.

12. The combination with a bushing insulator, of a conductor extending through said insulator, a transmission line connected with said conductor, a conductor cage surrounding said transmission line and insulated therefrom, a current transformer disposed within said bushing insulator and energized by said conductor, and means for supplying supplemental energizing current to said transformer from the condenser formed by said conductor cage and transmission line.

13. The combination with a bushing insulator, of a conductor extending' through said insulator and forming the primary winding of a current transformer disposed within said insulator, a magnetic core member for said current transformer, a secondary winding for said current transformer disposed within said insulator, a transmission line connected with said conductor, a conductor cage surrounding said transmission line and insulated therefrom, a supplemental primary winding disposed about the core member of said current transformer and having the terminals thereof connected respectively with said conductor cage and conductor.

14. The combination with a bushing insulator, of a conductor extending through said insulator and forming the primary winding of a current transformer arranged within said insulator, a magnetic core member for said current transformer, asecondary winding for said transformer, a transmission line connected with said conductor, a current transformer disposed outside of said insulator and energized by said transmission line, a condenser in series with the secondary Winding of said last named current transformer, a supplemental primary winding for the current transformer within said bushing insulator, and means for supplying current to said supplemental primary winding from the secondary winding of the current transformer outside of said-insulator.

15. The combination with a bushing insulator, of a conductor extending through said insulator and forming the primary of a current transformer disposed within said insulator, a magnetic core member for said current transformer, a secondary winding for said current transformer, a transmission line connected with said conductor, a supplemental primary winding for said current transformer, and a current transformer disposed outside of said insulator and energized by said transmissionline for supplying ourrent to said supplemental winding, said outside current transformer having a condenser in series with the secondary Winding thereof.

16. The combination with a bushing insulator, of a conductor extending through said insulator, a' transmission line connected with said conductor and disposed outside of said insulator, a transformer disposed within said bushing insulator, and means disposed outside of said insulator and energized from said transmission line for supplying an exciting current to said transformer.

17. The combination with a conductor, of a secondary winding forming with said conductor a transformer of which said conductor is the primary, a magnetic core for said transformer, and means for supplying a leading exciting current to said transformer.

18. Thecombination with a bushing insulator, of a conductor extending through said insulator and having a portion thereof arranged in a coil, the axis of which is parallel with the axis of said bushing insulator, a magnetic core for said coil, and means ineluding a condenser for supplying a supplemental exciting current to said transformer.

19. The combination with a conductor, of a magnetic core member arranged to be energized by alternating current flowing in said conductor, a secondary winding disposed in the magnetic field of said core mem ber, a correction winding for correcting the phase displacement of the current induced in said secondary winding, and means for supplying leading current to said correction winding.

20. The combination with a conductor, of a magnetic core member, means energized by alternating current flowing in said conductor for magnetizing said core member, a secondary winding disposed in the magnetic field of said core member, a condenser charged by alternating potential in said conductor, a correction winding for correcting the phase displacement of the current induced in said secondary winding, and means for directing the charging current for said condenser through said correction winding.

21. The combination with a bushing insulator, of a conductor extending through said insulator, a magnetic core member disposed within said insulator, means energized by alternating potential in said conductor for magnetizing said core member, a secondary winding disposed in the magnetic field of said core member, a condenser arranged to be charged by the potential in said conductor, a correction winding for correcting the phase displacement of the current induced in said secondary winding, and means for directing the charging current for said condenser through said correction winding.

22. The combination with a bushing insulator, of a conductor extending through said insulator, a magnetic core member disposed within said insulator and arranged to be magnetized by alternating current in said con-' ductor, a secondary Winding disposed within the magnetic field of said core member, a correction winding in circuit with said secondary winding, and means for supplyng a leading current to said correction winding.

23. The combination with a bushing insulator, of a conductor extending through said insulator, a magnetic core member disposed within said insulator, a magnetizing winding for said core member, a transformer in series with said conductor disposed outside of said insulator, the secondary of said transformer being connected with said magnetizing winding, and a secondary winding disposed in the field of said core member.

24:. The combination with a bushing insulator, of a conductor extending through said insulator, a magnetic core member disposed within said insulator, a magnetizing winding for said core member, a transformer in series with said conductor and disposed outside of said insulator, the secondary of said transformer being electrically connected to said magnetizing winding, a secondary winding disposed within said insulator within the field of said magnetic core member, a correction winding for correcting the phase displacement of the current induced in said secondary winding, a second transformer in series with said conductor disposed. outside of said insulator, and a condenser in circuit with the secondary winding of said second named transformer, said condenser and secondary winding being connected with said correction winding for supplying leading current thereto.

25. The combination with a bushing insulator, of a conductor extending through said insulator, a magnetic core member disposed within said conductor, a secondary winding disposed within said insulator and in the field of said magnetic core member, a correction winding surrounding said core member, a capacitance member disposed within said insulator, and a circuit for supplying charging current to said capacitance member, said correction winding being connected in said last named circuit.

26. The combination with a bushing insulator, of a conductor extending through said insulator, a magnetic core member disposed within said insulator, a coil surrounding said core member, a metallic sleeve disposed within said insulator, means for connecting said sleeve-through said coil to said conductor, and a secondary winding disposed within said insulator and energized by the magnetic field of said core member.

27. Thecombination with a bushing insulator, of a conductor extending through said insulator and having aseries winding therein, a magnetic core member disposed Within said series winding, a secondary winding disposed within the field of said core member and energized by said field, a condenser, and a correction winding for correcting the phase displacement of the current induced in said secondary winding, saidcorrection winding being electrically connected between said condenser and said conductor, the element of said condenser opposite said conductor being grounded.

In testimony whereof I have signed my name to this specification this 6th day of Sept.

ARTHUR O. AUSTIN. 

